Computational protocol: Tomographic Evaluation of the Lower Incisor's Bone Limits in Mandibular Symphysis of Orthodontically Untreated Adults

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Protocol publication

[…] The CBCT scans of 40 patients treated at a private orthodontic clinic (Proprium Dentistry, Santa Maria, Brazil) were evaluated. The research protocol was approved by the Research Ethics Committee (CEP) of the Federal University of Santa Maria (Santa Maria, RS, Brazil; CAAE: 53310316.0.0000.5346).All tomographic image exams were obtained with a Gendex GX CB-500 tomograph (Gendex Dental Systems, Hatfield, PA, USA) with standard settings (120 kVp, 5 mA, acquisition time of approximately 23 seconds, and a field of view that was 14 cm in diameter × 8 cm in height with 0.25 mm voxels). Both male and female adult patients were considered for inclusion. The inclusion criterion was to have four erupted lower incisors. The exclusion criteria included the following: patients who had previously undergone orthodontic or prosthetic treatment, present syndromes, or history of periodontal disease and poor image quality (artifacts or distortions).For tomographic evaluation, the images in Digital Imaging and Communications in Medicine (DICOM) format were imported into OsiriX (OsiriX Foundation, Geneva, Switzerland). Initially, a multiplanar reconstruction (MPR) was performed to obtain an image corresponding to a cephalometric radiograph profile, and facial growth pattern was determined by analyzing the facial height index (FHI) [], which is the ratio of the posterior facial height (PFH) to the anterior facial height (AFH) []. On the basis of FHI, facial growth patterns were classified as follows: hyperdivergent, FHI values lower than 0.649; normal, FHI values between 0.65 and 0.75; and hypodivergent, FHI values greater than 0.751. The same image was used to determine the inclination of the most projected lower central incisor by using the angle of inclination of the most projected lower incisor (IMPA) []. The skeletal anteroposterior relationship was determined by Wits analysis (AO-BO) [].To perform bone thickness measurements, MPRs were carried out through the center of the lower incisor root canal to obtain sagittal views that corresponded to the central portions of the lower incisors. A root canal image was used as a reference to standardize tracing of the long axis of the lower incisor. Root length was defined and measured as the distance from the cementoenamel junction to the apex. A line perpendicular to the long axis of the incisor was used to establish reference points: 0% of the root represented the cement enamel junction and 100% represented the apex. The following measurements were made in the sagittal section of the tomographic image: labial alveolar bone thickness, lingual alveolar bone thickness, total alveolar bone thickness, total mandibular symphysis thickness, and total mandibular symphysis height on the labial and lingual sides of the lower incisors ().Measurements of alveolar bone thickness on the labial and lingual sides of the lower incisor roots were performed in two predetermined locations. Lines perpendicular to the long axis of the lower incisor were drawn at 80% and 100% of root length. To determine the height of the entire mandibular symphysis, a line parallel to the long axis of the tooth was drawn from the point representing the bony base of the lower incisor to a line perpendicular to the long axis of the tooth and traced at the lowest point of the cortical bone of the mandibular symphysis on the labial and lingual sides. For mandibular symphysis thickness determination, a line was drawn perpendicular to the long axis of the tooth in the thickest portion of the mandibular symphysis ().The spatial resolution of the scans was determined by using an acrylic phantom (Gendex Dental Systems, Hatfield, PA, USA). The phantom's tomographic image was acquired with the same specifications as the patients' scans and in accordance with the manufacturer's recommendations. The spatial resolution of tomographic images was 0.7 mm.Repeating measurements twice for 20% of the sample with a 1-week interval between each evaluation assessed intraexaminer agreement and the results were excellent (ICC > 0.9) [].Statistical Package for the Social Sciences 20 (SPSS Inc., Chicago, IL, USA) was used for statistical analysis. Normality was analyzed by the Shapiro-Wilk test and correlations between bone measurements, FHI, IMPA, AO-BO, and patient age were analyzed using Pearson's correlation test.Out of 40 patients, 70% were female; 62.5% were skeletal Class I, 15% were Class II, and 22.5% were Class III. The mean age was 34.2 (±14.6) years. […]

Pipeline specifications

Software tools OsiriX, SPSS
Application Miscellaneous
Organisms Homo sapiens
Diseases Alveolar Bone Loss